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Monday’s medical myth: wearing tight undies will make you infertile

Tight underwear may increase scrotal temperature but there’s no evidence to show it reduces fertility. AAP

Most men have a preference for boxers or briefs, but which are better when it comes to fertility?

Many things can affect a man’s ability to make or transport sperm, including sexually transmitted infections, prostate and testicle infections, drug use, smoking, obesity and, perhaps surprisingly, heat.

Sperm are made in the testes (or testicles), a pair of egg-shaped glands that sit in the scrotum, in a lengthy and continuous process. It takes about 70 days for germ cells to develop into the mature sperm, found in semen, that can fertilise an egg.

Around one in 20 men have some kind of fertility problem, with low numbers of sperm in their ejaculate. But one in every 100 men produces no sperm at all.

Of the couples who present with fertility problems, almost half are due to fertility issues in the male partner only, or in both partners. It’s important to note, though, many men will still be able to father children naturally, even with have a lowered sperm count.

The location of the testes in the scrotum makes the testes vulnerable to trauma, but it serves a strategic purpose – to keep them around 2°C cooler than normal body temperature, which is required for the production of top-quality sperm.

Normally, the sweating of the scrotal skin serves as an “evaporative air cooling system” for the testes. But if it’s too hot and the scrotum can’t sweat, the testes will have trouble making sperm.

The scrotum needs to keep the testes 2°C cooler than the body to produce high-quality sperm. Gilberto Santo Rosa

If the testes are too hot for too long, sperm production is interrupted and won’t return to normal until their temperature returns to normal. It can take a few months of keeping the testicles at a normal temperature for sperm counts to improve if they have been lowered by heat stress.

Excess testicular heating can happen internally, as a result of feverish illnesses such as severe influenza. In cases such as these, there is no way to avoid the testes overheating because the core body temperature may be 40°C or more.

As for external testicular heating, this is more easily avoided by saying no to spas, saunas and hot baths.

While wearing tight-fitting underwear might seem to increase the temperature of the scrotum, there is no evidence to suggest it leads to infertility due to impaired sperm production.

A review of studies of genital heat stress on semen quality published in Andrologia (2007) found no conclusive link. The review looked into several aspects of heat stress, including more than 10 studies on wearing tight underwear and/or tight clothing.

The reviewed studies, from varied population groups and different methodologies, showed that while wearing tight-fitting underwear or clothing was associated with increased scrotal temperatures, there was no clear evidence that this resulted in reduced semen quality.

The upshot of all this is that more research is needed to answer the question of whether wearing tight underwear makes a significant contribution to fertility problems in men who would otherwise have normal sperm counts.

But for men with an already low sperm count who are trying to conceive, keeping the scrotum as cool as possible should give the testes the best chance to do their job. Keeping a pair or two of boxers on hand isn’t such a bad idea.

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